Such considerations show us the meaning of the subdivisions into which science has been arranged for convenience of study and research. They represent different aspects of nature, different sections, as it were, cut through the solid model which stands for the sum of all our scientific knowledge of the universe. The idea that a mechanical explanation of any known phenomenon is fundamental and complete may be traced to the familiarity of mechanical conceptions in our every day experience. The popular ideas of matter and force are not scientific definitions, but they lead to a false idea that the exact scientific concepts with the same names are understood. Matter is defined scientifically in terms of its mass or inertia, and is commonly known to us by our sense of touch, by its resistance to force. But the fact that we have a muscular sense, which gives us the impression of a force and so of mass and matter, is an accident of our bodies and minds. The electric fish or torpedo may have an electric sense, and a fish-philosopher might argue that it is more intelligible and satisfactory to explain mass in terms of electricity than electricity in terms of mass. Even to us, there seems now no reason to regard mechanics as philosophically the most fundamental science. It is merely one aspect from which we may regard any definite problem.
A nerve-impulse may be regarded from a psychological aspect when we deal with the thought which accompanied it ; from a physiological aspect when we examine its relation to other changes in the body. But modern methods have co-ordinated it also with definite chemical and electrical changes, and are said sometimes to have "explained" the nerve-impulse in physical terms. But, as always, an "explanation" proves to be simply a restatement of a phenomenon in terms of ideas which are already familiar to the mind, and therefore appear to be better understood. Nevertheless,
from our present point of view, no one of these possible aspects of the phenomenon—of the nerve-impulse—is essentially more fundamental than any other. To the psychologist the nerve impulse is expressed in terms of thought, to the physicist by physi cal changes. The fact that a thought is accompanied by move ment of matter or electricity does not make it less fundamental. The two manifestations appear together; there is "psychophysi cal parallelism." But the question of the connection between them cannot, at present at any rate, be answered by science. Now, and perhaps always, it is a problem for metaphysical speculation. BIBLIOGRAPHY.—General: G. Sarton, Introduction to the History of Science (vol. i. From Homer to Omar Khayyam, 1927) ; F. A. Lange, History of Materialism (Eng. trans., E. C. Thomas, 3rd ed., 1925) ; W. C. D. Dampier-Whetham, A History of Relations with Philosophy and Religion (1929).
Speczat Periods: T. Gomperz, Greek Thinkers (Eng. trans., L. Magnus, 1901) ; J. Masson, The Atomic Theory of Lucretius (1884) ; H. 0. Taylor, The Mediaeval Mind (2 vols., 1911) ; J. J. Fahie, Galileo, his Life and Work (1903) ; E. A. Burtt, The Metaphysical Foundations of Modern Science (1925) ; J. T. Merz, European Thought in the Nineteenth Century (4 vols., 1896-1914) ; Darwin and Modern Science (1909) ; W. C. D. Dampier-Whetham, The Recent Development of Physical Science (5th ed., 1924) ; A. N. Whitehead, Science and the Modern World (1927); E. N. da C. Andrade, The Scientific Significance of Lucretius (Introductory Essay to Munro's Lucretius, 4th edition), 1928. (C. D.-W.)